David Cameron and Nick Clegg tried to draw a line under the vitriolic and personal attacks of the Alternative Vote campaign yesterday in an attempt to rebuild confidence between Coalition partners before Thursday's referendum on electoral reform.

Despite previously condemning a "right-wing clique" behind the No campaign, the Liberal Democrat leader said he did not want to "personalise" the issue. Mr Cameron meanwhile insisted that both parties would continue to provide "strong and effective coalition government" regardless of the outcome of the referendum.

However, their show of unity was undermined only hours later by the Liberal Democrat Energy Secretary, Chris Huhne, who accused the Tories of being opposed to all progressive change including votes for woman and universal suffrage.

It has also emerged that David Cameron's director of communications appeared to break government rules on political advisers by contacting the BBC over its coverage of the AV referendum.

Senior Liberal Democrats were "furious" after learning that Craig Oliver contacted the corporation to ask for "clarification" over its coverage of the AV campaign. They believe Mr Oliver's intervention was designed to put pressure on the BBC to give the No2Av campaign a more favourable showing.

Under government rules, special political advisers like Mr Oliver – who are paid by the taxpayer – are not allowed to participate in the No2Av campaign which must be run by party officials.

Yesterday – publicly at least – both Mr Clegg and Mr Cameron insisted that the AV referendum had not damaged the Coalition and that, regardless of the result, the business of government would not be affected. Supporters on both sides have been warned not to "gloat" if they win on Friday while at series of initiatives are being planned to distract attention from the fall-out of the vote. "We have long known that the period between the referendum result and the summer recess of Parliament will be the most difficult for both sides," said a government source.

Speaking in carefully co-ordinated consecutive interviews on the Andrew Marr show yesterday, Mr Clegg first insisted that his party would remain committed to the Coalition regardless of the result. "David Cameron and I, every day of every week, thrash out our differences within government. We are different leaders of different parties, we have different values we always will do. I think in many respects people have forgotten that sometimes because we have to work together in harness for the national good, as we will continue to do so for five years."

Mr Cameron later added: "The business of government goes on. Dealing with the deficit, reforming welfare, making sure there's quality schools for all our children. These things are going on even as the referendum and the local elections campaign take place."

However the show of unity was somewhat undermined by Mr Huhne, who used an interview later in the day to attack the Tory stance on AV.

Meanwhile in a speech today the Labour leader, Ed Miliband, will argue that the policies being pursued by the Coalition do not have a democratic mandate – as they were not backed by the majority of voters.

"Labour lost last year's general election but the Tories did not win it," he said. "It is extraordinary that since then they have repeatedly claimed that they won a mandate, and felt bold enough to force right-wing policies through Parliament; policies which weren't even in the Conservative manifesto, such as the top-down re-organisation of the NHS and front-line cuts to police."

Downing Street did not not deny that Mr Oliver had spoken to the BBC about the AV campaign. A statement said: "Part of the director of communications' role is to ensure that the Prime Minister's position is understood and in doing so he operates within the special advisers' code."